I have a 1997 Taurus GL wagon and sitting at a light it will die or the idle will go up to 1500 rpm. i have changed the IAC valve and checked for vacuum leaks. there are none. this is at the point can't drive car.. any ideas

OK i think after 50+ years of working on cars that i can detect a vacuum leak. the computer was not showing any codes at all. however i did finally find the problem. it was a worn out and very sloppy Throttle Sensor..